Wireless communication networks, such as the 3rd Generation (3G) and 4th Generation (4G) of wireless telephone standards and technology, are well known. Examples of such 3G and 4G standards and technology are the Universal Wireless Telecommunications System (UMTS™) and the Long Term Evolution (LTE) respectively, developed by the 3rd Generation Partnership Project (3GPP™) (www.3gpp.org).
These 3rd and 4th generations of wireless communications, have generally been developed to support macro-cell wireless phone communications, and more recently femto-cell wireless phone communications. Here the ‘phone’ may be a smart phone, or another wireless or portable communication unit that is linked wirelessly to a network through which calls etc. are connected. Henceforth all these devices will be referred to as wireless communication units. Calls may be data, video, or voice calls, or a combination of these.
Typically, wireless communication units, or User Equipment (UE) as they are often referred to in 3G parlance, communicate with a Core Network of the 3G or 4G wireless communication network. This communication is via a Radio Network Subsystem. A wireless communication network typically comprises a plurality of Radio Network Subsystems. Each Radio Network Subsystem comprises one or more cells, to which wireless communication units may attach, and thereby connect to the network. A base station may serve a cell. Each base station may have multiple antennas, each of which serves one sector of the cell.
Geolocation is the real-world geographical location of objects, and geolocation of wireless communication units is an increasingly important and desirable service. There are many mechanisms by which users of a wireless communication network may be located, whilst they are using the system. These include use of the global positioning system (GPS), if the wireless device is equipped with a GPS receiver and the user has enabled this on his/her device. However, many users do not enable GPS on their devices as it is typically a significant power drain on the device's battery. Other techniques examine the base-stations which are visible to a user's device and calculate the intersection of the coverage footprints of these base-stations, for example based upon drive-testing or data collected from previous users of the same base-stations who have had GPS enabled on their devices. The assumption is that the user device must be somewhere within the overlap of the coverage areas. Still other techniques measure the timing delay between a user device and a number of local base-stations; the time taken for signals to propagate to each base-station gives an estimate of the distance of the user device from each base-station and hence the combined information from a number of base-stations provides a set of ‘contours’ which intersect to provide the approximate location of the user.
These known geolocation techniques can work well in relation to wireless devices that are located outdoors. However, it is a much more difficult problem when devices are located indoors due to the attenuating effect of walls etc. GPS signals, for example, will not propagate very far at all within a building meaning that unless the user is located very close to a window, their location cannot be reliably ascertained by this means. Likewise, fewer base-stations will be ‘visible’ to a user device when the user is indoors, and this can make timing or coverage-overlap based geolocation mechanisms difficult to use. Ascertaining whether a device is located indoors or outdoors would make geolocating a wireless device a simpler process.
The ability to determine whether wireless devices connected to a wireless communication network are located indoors or outdoors would also enable indoor/outdoor wireless traffic patterns to be analysed in order to help plan and configure network coverage and load parameters for the wireless communication network more effectively. In particular, there is increasing focus being placed upon how best to serve indoor users, since a significant number of users spend a significant amount of time using wireless devices indoors, as the traditional land-line telephone is gradually consigned to history. Operators want to ensure that such users are well served and do not place an undue burden on the macro-cell network, which is expensive to expand in terms of additional capacity. Where large densities of indoor users are found, these could be better served by the placement of a small cell within, for example, the building, or outside the building but with antennas directed into the building.
FIG. 1 shows a typical indoor geolocation scenario based upon GPS geolocation. As noted above, GPS is of limited use within a building, only working (if at all) close to a window or similar aperture. A ‘radius of location uncertainty’ may be defined for a geolocation system. This is the radius of a circle, centred upon the reported location ‘fix’, within which a user could actually be located: the more accurate the geolocation system, the smaller the radius of location uncertainty, with the radius being zero for a ‘perfect’ geolocation system. GPS is typically very accurate, with a radius of location uncertainty (r1) of only a few meters under the most favourable operating circumstances (i.e. multiple observed GPS satellites, etc.). With this level of accuracy, it is relatively easy to differentiate between likely indoor and outdoor users simply on the basis of their reported location. GPS is, however, often not available, either through GPS chipsets being turned off inside mobile devices to reduce battery consumption, or due to obstructions caused by tall buildings or through the user being located well within the body of a building.
FIG. 2 shows a geolocation scenario involving one of the terrestrial geolocation techniques discussed above. For the purposes of this discussion, it does not matter which technique is being used, only that the radius of uncertainty, r2, is sufficiently large that the user could conceivably be located within or outside of a building and the geolocation system (unaided) is unable to distinguish between the two scenarios. The typical accuracy of a good terrestrial geolocation system, based upon a cellular telephone network (say), is around 100 m (i.e. r2=100 m) or greater. This is clearly insufficient to reliably place a user within or outside of a typical building.